JP4930201B2 - Internal combustion engine spark plug - Google Patents

Description

  The present invention relates to an ignition plug disposed in a combustion chamber of an internal combustion engine, and more particularly, to an ignition plug for an internal combustion engine having a configuration in which a center electrode and a ground electrode are disposed to face each other.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-313523, a spark plug including a center electrode and a ground electrode is known. Conventional spark plugs are configured such that a concave groove is formed in the front end surface of the center electrode facing the ground electrode, and spark discharge is likely to occur between these electrodes.

  In other words, the open end of the concave groove that opens to the tip surface of the center electrode is an edge portion that is pointed at a right angle. For this reason, when a voltage is applied between the center electrode and the ground electrode, discharge tends to occur starting from an edge portion where the electric field strength is increased. As a result, in the prior art, the voltage (required voltage) required for driving the spark plug is reduced.

JP 2002-313523 A

  In the prior art, a concave groove is formed in the front end surface of the center electrode to reduce the required voltage of the spark plug. However, in general, when the spark plug is repeatedly used, the edge portion of the center electrode is gradually worn and rounded, and the required voltage of the plug increases accordingly. When the wear of the center electrode proceeds and the edge portion disappears, for example, the required voltage of the spark plug exceeds the practical applied voltage, so that no spark discharge occurs.

  In this case, in the prior art, although a certain amount of edge portion can be formed by the concave groove, the amount of edge portion (length, number, etc.) is limited depending on the area of the tip surface of the center electrode, etc. It will be a thing. Thus, in the prior art, there is a limit to the amount of formation of the edge portion, and thus there is a problem that it is difficult to sufficiently improve the durability of the spark plug.

  The present invention has been made to solve the above-described problems, and can ignite an internal combustion engine that can hold the edge portion of the center electrode for a long period of time and can improve durability and extend its life. The purpose is to provide a plug.

A first invention comprises a center electrode provided in a combustion chamber of an internal combustion engine,
A ground electrode disposed opposite to the center electrode and performing a spark discharge with the center electrode;
A preliminary edge portion that is provided on the center electrode and appears as a sharp edge when the center electrode is worn by spark discharge;
It is provided with.

  According to the second invention, the central electrode is formed of a porous metal material having a plurality of pores, and the preliminary edge portion is a peripheral wall of each of the pores opened at a site where the central electrode is worn. It consists of parts.

  According to a third aspect of the invention, the center electrode is formed by laminating a plurality of metal plates having through holes, and the preliminary edge portion is a peripheral wall of each through hole that opens at a site where the center electrode is worn. It consists of parts.

  According to a fourth aspect of the present invention, the center electrode is formed by bundling and integrating a plurality of metal wires, and the preliminary edge portion of each metal wire projecting when the adjacent metal wires are worn out. It is comprised by the front-end | tip part.

  According to a fifth invention, the center electrode includes a cylindrical binding member that surrounds and binds the plurality of metal wires from the outer peripheral side.

  According to a sixth aspect of the invention, the center electrode and the ground electrode are each formed in a columnar shape and are opposed in the axial direction, and the outer diameter of the center electrode is larger than the outer diameter of the ground electrode. Forming.

A seventh invention comprises a center electrode provided in a combustion chamber of an internal combustion engine,
A ground electrode disposed opposite to the center electrode and performing a spark discharge with the center electrode;
A plurality of edge portions provided on the center electrode and arranged over a position far from a position close to the ground electrode;
It is provided with.

  According to an eighth aspect of the invention, the center electrode is formed by laminating a plurality of metal plates so that the peripheral portions of adjacent metal plates are shifted from each other, and the plurality of edge portions are formed of the respective metals. It is comprised by the peripheral part of the board.

A ninth invention comprises a columnar center electrode provided in a combustion chamber of an internal combustion engine,
A ground electrode disposed opposite to the center electrode and performing a spark discharge with the center electrode;
A spiral edge provided on the center electrode and extending in the length direction while circling the outer periphery of the center electrode;
It is provided with.

  According to the first invention, when the spark plug is operated, a spark discharge can be performed between the center electrode and the ground electrode. And when a center electrode is worn out by electric discharge, the spare edge part arrange | positioned at a wear site | part or its vicinity can be made to appear as a new edge part. For this reason, the center electrode can be smoothly discharged with the edge portion always present. Therefore, the required voltage of the spark plug can be prevented from increasing as the center electrode is worn, and the required voltage can be stabilized over a long period of time. Thereby, durability of a spark plug can be improved and the lifetime can be extended.

  According to the second invention, the center electrode can be formed of a porous material, and the peripheral wall portion of the hole can be used as a spare edge portion. For this reason, when the center electrode is worn by electric discharge, a part of the holes existing inside the electrode can be opened at the worn part, and the peripheral wall part of the opened hole can function as an edge part. it can.

  Therefore, for example, a large number of preliminary edge portions can be efficiently formed using the pores of the porous material without performing mechanical processing or the like. In addition, since a large number of spare edge portions can be easily secured as compared with mechanical processing or the like, the life of the center electrode can be sufficiently extended.

  According to the third invention, for example, even if the center electrode has a complicated internal structure, the center electrode can be efficiently formed by laminating the metal plates. A plurality of through holes can be easily scattered inside the center electrode, and the peripheral wall portion of these through holes can be used as a spare edge portion. For this reason, when the center electrode is worn by electric discharge, a part of the through hole can be opened at the worn portion, and the peripheral wall portion of the opened through hole can function as an edge portion.

  According to the fourth invention, the central electrode can be formed by bundling a plurality of metal wires, and the tip of each metal wire can be used as a spare edge. And when the front-end | tip part of a certain metal wire is worn, the front-end | tip part of the other metal wire adjacent to this can be made to project relatively, and this projecting front-end | tip part can be functioned as an edge part. . Therefore, a center electrode having a plurality of spare edge portions can be easily realized without providing a special structure inside the center electrode, and the structure of the electrode can be simplified.

  According to the fifth invention, by using the binding member, it is possible to easily combine a plurality of metal wires, and to efficiently form the center electrode. Further, the strength and durability of the center electrode can be increased by the binding member.

  According to the sixth invention, for example, when a hole, a through hole, or the like is arranged inside the center electrode or the center electrode is formed of a plurality of wires, the substantial volume of the center electrode is reduced. There is only concern about a decrease in wear resistance. In this case, the substantial volume of the center electrode can be increased by making the outer diameter of the center electrode larger than that of the ground electrode. Therefore, even with a structure in which there is a gap inside the electrode, the wear resistance of the center electrode can be sufficiently enhanced.

  According to the seventh invention, the center electrode can be provided with a plurality of edge portions from a position far from the position close to the ground electrode. As a result, when the edge portion closest to the ground electrode is worn by discharge, the next closest edge portion can function as a starting point of discharge. For this reason, the center electrode can be smoothly discharged with the edge portion always present. Therefore, the required voltage of the spark plug can be stabilized for a long time without providing a special structure inside the center electrode, and the durability and life of the plug can be improved.

  According to the eighth invention, when the center electrode is formed, the plurality of edge portions are efficiently obtained by simply laminating the peripheral portion of each metal plate with respect to the adjacent metal plate while laminating the plurality of metal plates. Can be well formed.

  According to the ninth aspect, the spirally extending edge portion can be provided on the outer peripheral side of the center electrode. Thereby, when the center electrode is worn from the front end side, the extending direction of the edge portion is inclined obliquely with respect to the wear progressing direction. As a result, at the boundary position between the wear part and the non-wear part, the corner of the edge part can be made easier to stand as compared with the case where the edge part extends in the wear progressing direction. For this reason, the center electrode can smoothly discharge in a state where the corner of the edge portion exists on the tip side. Therefore, the required voltage of the spark plug can be stabilized for a long time without providing a special structure inside the center electrode, and the durability and life of the plug can be improved.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an overall view for explaining the configuration of a spark plug 10 according to the first embodiment. A spark plug 10 shown in FIG. 1 includes a metal housing 12 attached to a cylinder head (not shown) of an internal combustion engine.

  Here, the housing 12 is formed as a cylindrical body that is open on both sides in the axial direction, and a threaded portion 12a that is screwed onto the cylinder head is provided on the circumferential side thereof. Further, a substantially L-shaped electrode support portion 12b made of a metal material is integrally formed on the front end side of the housing 12. The electrode support portion 12b extends in the axial direction from the distal end side of the housing 12, and is bent radially inward in the middle of the length direction.

  2 is also used to describe the internal structure of the spark plug 10. On the inner peripheral side of the housing 12, an electrode support 16 is provided via a substantially cylindrical insulator. The electrode support 16 is formed in a rod shape with a conductive material, and a terminal portion 16b (see FIG. 1) connected to an ignition control circuit (not shown) or the like on the internal combustion engine side is provided on the base end side thereof. ing. Further, a substantially conical pedestal portion 16a is provided on the distal end side of the electrode support 16, and a center electrode 18 disposed in the combustion chamber of the internal combustion engine is fixed to the distal end surface of the pedestal portion 16a. .

  The center electrode 18 is made of, for example, an alloy containing iridium as a main component, and is formed in a columnar shape or a prismatic shape. The center electrode 18 protrudes in the axial direction from the pedestal 16 a of the electrode support 16 toward the ground electrode 20.

  On the other hand, the ground electrode 20 is made of substantially the same metal material as the center electrode 18 and is formed in a columnar or prismatic shape. The ground electrode 20 is fixed to the electrode support portion 12 b of the housing 12 and protrudes in the axial direction toward the center electrode 18. In this state, the center electrode 18 and the ground electrode 20 are disposed coaxially with respect to the axis OO. The front end surface 18a of the center electrode 18 and the front end surface 20a of the ground electrode 20 are opposed to each other with a discharge gap G that is a gap dimension in the axial direction interposed therebetween.

[Characteristics of Embodiment 1]
Next, the structure of the center electrode 18 which is a characteristic part of the first embodiment will be described with reference to FIG. The center electrode 18 is formed as a columnar body having a porous structure, and a large number of pores 22 are present at irregular positions therein. Some of these holes 22 are open in the tip surface 18a when the center electrode 18 is not worn. The peripheral wall portion of the opened hole 22 forms a sharp edge portion 24.

  On the other hand, the other holes 22 located away from the tip surface 18a are arranged inside the center electrode 18 in the initial state. The peripheral wall portions 26 of these holes 22 constitute a preliminary edge portion that appears as a new edge portion on the front end face 18a when the front end side of the center electrode 18 is worn by discharge. In other words, the shape of the transverse cross section (cross section perpendicular to the axis OO) of the center electrode 18 is configured to discontinuously change with respect to the direction of wear due to the presence of the holes 22. . And this discontinuous part becomes a preliminary | backup edge part.

  Here, when the center electrode 18 is formed in a porous structure, there is a concern that the wear resistance may be reduced due to a decrease in the volume of the electrode. For this reason, in the present embodiment, the outer diameter D of the center electrode 18 is formed to be sufficiently large, and the substantial volume of the center electrode 18 is set to be equal to that of the conventional one. More specifically, the outer diameter dimension D of the center electrode 18 is set as a dimension value larger than the outer diameter dimension d of the ground electrode 20 as shown in the following equation (1).

(Equation 1)
D> d

  Thereby, even when the center electrode 18 has a porous structure, high wear resistance can be realized. Even when the outer diameter dimension D is increased, the substantial volume of the center electrode 18 is the same as the conventional volume, so that the phenomenon (cooling loss) in which the flame nucleus formed during discharge is cooled by the center electrode 18 It can be suppressed to the same level as before.

[Operation of Embodiment 1]
(Ignition operation in the initial state)
When the spark plug 10 is used, the center electrode 18 is connected to the ignition control circuit via the electrode support 16 and the like. The ground electrode 20 is grounded to the cylinder head of the internal combustion engine via the housing 12. In this state, when a high voltage is applied between the center electrode 18 and the ground electrode 20 by the ignition control circuit, a spark discharge is generated between the electrodes 18 and 20. Thereby, the spark plug 10 can ignite the air-fuel mixture in the combustion chamber of the internal combustion engine.

  Here, a sharp edge portion 24 is formed on the distal end surface 18a of the center electrode 18 by a plurality of open holes 22 even in an initial state in which no wear occurs. When a high voltage is applied between the center electrode 18 and the ground electrode 20, the electric field strength is increased at the edge portions 24 as compared with the surroundings. For this reason, the center electrode 18 can smoothly start the spark discharge when the edge portion 24 closest in potential to the ground electrode 20 becomes the starting point of the discharge.

(When the center electrode 18 is worn)
FIG. 4 shows a state where the wear of the center electrode 18 has progressed as the spark plug 10 repeats the discharge. Thus, when wear progresses on the tip side of the center electrode 18, the tip surface 18a of the electrode has a rounded shape, and the edge portion 24 that existed in the initial state disappears. However, in this case, a part of the hole 22 existing in the center electrode 18 opens in the tip surface 18a of the electrode. The peripheral wall portion 26 (preliminary edge portion) of the hole 22 forms a new edge portion 24 ′ at a position surrounding the opening portion of the hole 22.

  As described above, the peripheral wall portions 26 of the numerous holes 22 existing inside the center electrode 18 become new edge portions 24 'as the electrode wear progresses, and successively on the front end surface 18a of the center electrode 18. Appear. Therefore, the edge part 24 used as the starting point of spark discharge always existed in the front end surface 18a of the center electrode 18. FIG.

[Effect of Embodiment 1]
As described above, according to the present embodiment, the center electrode 18 is formed of a porous material. Therefore, the peripheral wall portion 26 of the hole 22 existing inside the center electrode 18 can be used as a spare edge portion. When the center electrode 18 is worn out by discharge, the holes 22 disposed in the wear site or in the vicinity thereof can be opened at the wear site, and the peripheral wall portion 26 of such a hole 22 can be newly opened. The edges 24 'can appear one after another.

  Thereby, the center electrode 18 can smoothly discharge in a state where the edge portion 24 ′ (or the edge portion 24) always exists. Therefore, the required voltage of the spark plug 10 can be prevented from increasing as the center electrode 18 wears, and the required voltage can be stabilized over a long period of time. As a result, the durability of the spark plug 10 can be increased and the life thereof can be extended.

  Further, since the center electrode 18 is formed of a porous material, for example, a large number of peripheral wall portions 26 can be efficiently formed using the internal holes 22 without performing mechanical processing or the like. In addition, since the large number of peripheral wall portions 26 can be easily secured as compared with mechanical processing or the like, the life of the center electrode 18 can be sufficiently extended.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Characteristics of Embodiment 2]
FIG. 5 shows the center electrode 32 of the spark plug 30 according to the present embodiment. The center electrode 32 is formed by laminating and joining a plurality of metal plates 34 along the axis OO, and as a whole, for example, has a cylindrical shape.

  Here, a plurality of through holes 36 are formed in each metal plate 34 as shown in FIG. For this reason, a through hole 36 of the metal plate 34 located at the foremost end is opened at the distal end surface 32 a of the center electrode 32. The peripheral wall portions (open ends) of these through holes 36 form a sharp edge portion 38 in the initial state.

  Further, the through holes 36 of the respective metal plates 34 are arranged so as to be shifted from the through holes 36 of the adjacent metal plates 34 (so as not to overlap completely). In this case, when the center electrode 32 is formed, a plurality of types of metal plates 34 having different formation positions of the through holes 36 may be stacked. Further, while laminating the same kind of metal plates 34, the positions of the through holes 36 are shifted with respect to the adjacent metal plates 34 by appropriately rotating the metal plates 34 around the axis OO. Also good.

  As a result, a plurality of small spaces are formed in the center electrode 32 by the respective through holes 36 in substantially the same manner as in the case of the holes 22 in the first embodiment. The peripheral wall portions 40 of these through holes 36 constitute a preliminary edge portion that appears on the tip surface 32a as a new edge portion 38 'when the tip side of the center electrode 32 is worn.

[Effect of Embodiment 2]
In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first embodiment. That is, when the center electrode 32 is worn by electric discharge, a part of the through hole 36 can be opened at the worn portion, and the peripheral wall portion 40 of the opened through hole 36 can function as the edge portion 38 '. .

  In addition to this, in the present embodiment, the center electrode 32 is formed by a plurality of metal plates 34. For this reason, even if it is the center electrode 32 which has a complicated internal structure, the center electrode 32 can be efficiently formed by laminating | stacking the metal plate 34, for example. A plurality of through holes 36 corresponding to the preliminary edge portions can be easily scattered in the center electrode 32.

  Next, Embodiment 3 of the present invention will be described with reference to FIG. 7 and FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Characteristics of Embodiment 3]
FIG. 7 shows the center electrode 52 of the spark plug 50 according to the present embodiment. The center electrode 52 is formed by bundling and integrating a plurality of metal wires 54, and as a whole, for example, has a cylindrical shape centered on the axis OO.

  Here, a bundling member 56 formed in a cylindrical shape by a metal material is provided on the outer peripheral side of each metal wire 54. The binding member 56 surrounds and binds the metal wires 54 as a whole. Moreover, each metal wire 54 is formed, for example, in a uniform length in the initial state. For this reason, in the initial state, the outer periphery on the distal end side of the binding member 56 forms an annular edge portion 58.

  Further, the pointed tip portion 60 of each metal wire 54 is arranged on the same plane as the tip surface 52 a of the center electrode 52. As shown in FIG. 8, these tip portions 60 constitute a spare edge portion that appears on the tip surface 52a as a new edge portion 58 'when the tip side of the center electrode 52 is worn. That is, when the tip 60 of a certain metal wire 54 is worn, the tip 60 of another metal wire 54 adjacent to the metal wire 54 becomes a new edge 58 'projecting relatively, so that the edge 58' Can appear one after another.

[Effect of Embodiment 3]
In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first embodiment. In addition to this, in the present embodiment, since the center electrode 52 is formed of the metal wire 54, the front end portion 60 of each metal wire 54 can be used as a spare edge portion. Therefore, the center electrode 52 having a plurality of tip portions 60 can be easily realized without providing a special structure inside the center electrode 52, and the structure of the electrode can be simplified.

  In addition, since the cylindrical binding member 56 is provided on the outer peripheral side of each metal wire 54, a plurality of metal wires 54 can be easily combined by the binding member 56, and the center electrode 52 can be efficiently formed. it can. Further, the binding member 56 can increase the strength and durability of the center electrode 52.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. 9 and FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Characteristics of Embodiment 4]
FIG. 9 shows the center electrode 72 of the spark plug 70 according to the present embodiment. The center electrode 72 is formed by, for example, laminating and joining a plurality of circular metal plates 74 along the axis OO.

  In this case, each metal plate 74 has a pointed annular peripheral portion located between the surface and the side surface (outer peripheral surface). And the peripheral part of the metal plate 74 which comprises the front end surface 72a of the center electrode 72 forms the edge part 76 in an initial state. Further, as shown in FIG. 10, the peripheral portions of the respective metal plates 74 are arranged so as to be shifted from the peripheral portions of the adjacent metal plates 74 (so as not to overlap completely).

  As a result, a plurality of edge portions 76 are formed on the center electrode 72 by the peripheral edge portion of each metal plate 74. These edge portions 76 are arranged side by side in the direction of the axis OO of the center electrode 72 over a position far from a position close to a ground electrode (not shown).

[Effect of Embodiment 4]
In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first embodiment. That is, when the edge portion 76 closest to the ground electrode is worn by discharge, the next edge portion 76 can function as a starting point of discharge. For this reason, the center electrode 72 can smoothly discharge in a state where the edge portion 76 always exists.

  In addition to this, in the present embodiment, the center electrode 72 is formed by a plurality of metal plates 74. For this reason, when the center electrode 72 is formed, the plurality of edge portions 76 are efficiently formed by simply laminating the peripheral portions of the individual metal plates 74 with respect to the adjacent metal plates 74 while laminating the metal plates 74. be able to. Moreover, since it is not necessary to provide a special structure inside the center electrode 72, the structure of the electrode can be simplified.

  Next, a fifth embodiment of the present invention will be described with reference to FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Characteristics of Embodiment 5]
FIG. 11 shows the center electrode 82 of the spark plug 80 according to the present embodiment. The center electrode 82 is formed as a columnar body centered on the axis OO and protrudes toward a ground electrode (not shown). The tip surface 82a of the center electrode 82 is formed in a star shape having, for example, five sharp corners 82b.

  Further, for example, five edge portions 84 projecting in the radial direction are provided on the outer peripheral surface of the center electrode 82. The edge portions 84 spirally circulate around the outer peripheral side of the center electrode 82 while extending in the axis OO direction starting from each corner portion 82b of the tip end surface 82a.

[Effect of Embodiment 5]
Thus, according to the present embodiment, the center electrode 82 is provided with the spiral edge portion 84. Thereby, when the center electrode 82 is worn from the front end side, the extending direction of the edge portion 84 can be inclined obliquely with respect to the wear progressing direction. As a result, at the boundary position between the wear part and the non-wear part, the corner of the edge part 84 can be made easier to stand as compared with the case where the edge part 84 extends in the progressing direction of wear.

  For this reason, the center electrode 82 can smoothly discharge in a state where the corner of the edge portion 84 exists on the tip side. Therefore, even if a special structure is not provided inside the center electrode 82, the required voltage of the spark plug 80 can be stabilized over a long period of time, and the durability and life of the plug can be improved.

  In the first embodiment, the outer diameter D of the center electrode 18 is set larger than the outer diameter d of the ground electrode 20. In this case, also in Embodiments 2 to 5, the outer diameter of the center electrodes 32, 52, 72, and 82 may be made larger than the outer diameter of the ground electrode.

  In the second embodiment, each metal plate 34 is provided with a circular through hole 36. However, the present invention is not limited to this, and a configuration in which a through-hole having a shape other than a circle having a polygonal shape, for example, may be provided. In addition, the present invention may be configured such that through holes are provided only in some of the metal plates as necessary, for example, as a configuration in which metal plates having through holes and metal plates having no through holes are alternately stacked. Also good.

  In the second and fourth embodiments, the case where the circular metal plates 34 and 74 are stacked has been described as an example. However, the present invention is not limited to this, and a configuration in which metal plates having a shape other than a circle, such as a polygonal shape, an elliptical shape, a star shape, a cross shape, and a U-shape, are stacked. Furthermore, this invention is good also as a structure which laminates | stacks several types of metal plate from which a shape differs.

1 is an overall view showing an ignition plug of an internal combustion engine according to Embodiment 1 of the present invention. It is an expanded sectional view showing the state where the tip side of the spark plug was broken along the axial direction of the center electrode. It is a principal part expanded sectional view in FIG. 2 which shows a center electrode. It is a principal part expanded sectional view which shows the state which the center electrode was worn out. It is a partial expansion perspective view which shows the center electrode of the ignition plug of the internal combustion engine by Embodiment 2 of this invention. It is a disassembled perspective view which shows the state which laminates | stacks several metal plates and forms a center electrode. It is a partial expansion perspective view which shows the center electrode of the ignition plug of the internal combustion engine by Embodiment 3 of this invention. When the front end side of the center electrode is worn, it is an enlarged cross-sectional view showing the worn portion in a state of being broken along the axial direction. It is a partial expansion perspective view which shows the center electrode of the ignition plug of the internal combustion engine by Embodiment 4 of this invention. It is a disassembled perspective view which shows the state which laminates | stacks several metal plates and forms a center electrode. It is a partial expansion perspective view which shows the center electrode of the ignition plug of the internal combustion engine by Embodiment 5 of this invention.

Explanation of symbols

10, 30, 50, 70, 80 Spark plug 12 Housing 12a Screw portion 12b Electrode support portion 14 Insulator 16 Electrode support body 16a Base portion 16b Terminal portions 18, 32, 52, 72, 82 Center electrodes 18a, 20a, 32a, 52a, 72a, 82a Tip surface 20 Ground electrode 22 Holes 24, 24 ', 38, 38', 58, 58 ', 76, 84 Edge portion 26, 40 Peripheral wall portion (preliminary edge portion)
34, 74 Metal plate 36 Through hole 54 Metal wire 56 Bundling member 60 Front end (preliminary edge)
G discharge gap D outer diameter of center electrode 18 d outer diameter of ground electrode 20

Claims (2)

A central electrode provided in the combustion chamber of the internal combustion engine;
A ground electrode disposed opposite to the center electrode and performing a spark discharge with the center electrode;
Provided at the center electrode, and when the center electrode is worn by spark discharge, a preliminary edge portion that appears as a sharp edge portion, and
The center electrode is formed of a porous metal material having a plurality of pores, and the preliminary edge portion is a peripheral wall portion of each of the pores opened to a portion where the center electrode is worn. A spark plug for an internal combustion engine. Wherein the center electrode and the ground electrode, each formed in a columnar shape and configuration to be opposed in the axial direction, the outer diameter of the center electrode is made of formed larger than the outer diameter of the ground electrode according to claim 1 ignition plug of an internal combustion engine according to.

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